Lasers emit coherent beams of electromagnetic energy, including a wide range of light wavelengths, among which are the visible (from red to violet) light wavelengths which can safely be viewed by a person without requiring that the person wear goggles.
The aforementioned, commonly-owned U.S. Pat. Nos. 5,090,789 and 5,311,335, incorporated by reference herein, describe a laser light show device and method. Laser light shows are typically use laser light sources to project brilliantly colored light patterns upon some reflective surface and, by changing the patterns, an appearance of an image having three-dimensionality is created. In the aforementioned patents, it is taught that the coherent nature of laser beams can advantageously be employed to form true (rather than apparent) three-dimensional images. Among the features discussed in these patents is that object image information signals can be supplied to the lasers by an object image information source which can contain virtually any type of image data. For example, the object image information signals can represent graphics data, such as that used in an engineering workstation, a video game or medical imaging applications.
The aforementioned commonly-owned, copending U.S. patent application Ser. No. 08/152,861, now U.S. Pat. No. 5,572,375, describes systems for generating and displaying true volumetric images. Generally, as described therein, a volumetric (three-dimensional) image is generated, then translated (spatially moved) by physical optical elements to a viewing position.
Most laser displays are merely two-dimensional projections on a two-dimensional surface. Some techniques, such as that described in U.S. Pat. No. 5,148,310, provide a depth component by rapidly spinning or oscillating the two dimensional surface. These techniques, however suffer from point-addressability, viewability, mechanical stability and interactionability problems and shortcomings.
It has long been known in the art that an auto-stereoscopic, three-dimensional volume display can be created by imposing a two-dimensional image on an imaging surface or display screen and the rapidly moving the imaging surface along a third axis. In the method of imaging known as direct volume display devices (DVDDs), the display screen is oriented so as to cause the image on the screen to sweep through the desired volume of space. One such system is described in U.S. Pat. No, 3,140,415 ("Ketchpel") which utilizes a phosphorescent rotating screen being illuminated by fixed electron gun means. Serious drawbacks to such a system, related to the lag time of the phosphors have been discussed in detail in U.S. Pat. No. 4,799,103 ("Muckerheide"). Additional drawbacks to such a system arise from the requirement of enclosing the screen and electron gun means in a vacuum. Muckerheide also discusses the evolution of the art towards incorporating lasers as image generation sources. Currently, such use of lasers is widely practiced and is generally preferred.
In general, all of these attempts at generating three-dimensional images utilize two-dimensional image projection techniques with mechanical scanning to produce the illusion of a third dimension. Because of present scanning methods and their limited scanning speed, image complexity must be limited to avoid excessive flicker. With these techniques, the use of phosphorescent screens to improve persistence of the image merely causes the image to smear in space. Moreover, the mechanical nature of these display devices creates stability problems as well as update rate limitations.
U.S. Pat. No. 5,148.310 ("BATCHKO"), incorporated by reference herein, describes a rotating, flat screen, fully addressable volume display system, which incorporates a rotating flat screen upon which is projected a two-dimensional scanned image. The image is changed as the screen is rotated, the rotation of the screen adding a third dimension to the sequence of two-dimensional images projected thereon. When the screen is rotated at sufficient speed, the phenomenon of visual persistence (in the viewer's eye) gives the sequence of two-dimensional images the appearance of a three-dimensional image in a full cylindrical volume of space. A system of reflectors, rotating in unison with the screen, is positioned between the screen and the two-dimensional image generator to allow the two-dimensional image to strike the surface of the rotating screen at a constant angle throughout the screen's rotation. The display is capable of being presented in color and is updatable in real time.
In BATCHKO, the size of the image created by the apparatus is limited to the diameter of the cylinder within which the screen rotates, and the position of the image is limited to the location of the cylinder (i.e., the image will appear to be in the cylinder). If the cylinder is small (e.g., having a diameter up to approximately one foot or one-third meter), permitting a commensurately small image to be displayed, the device would be portable and suitable, for example, for use as an output device for a personal computer. If the cylinder is large (e.g., having a diameter of several feet or meters), permitting a commensurately large image to be displayed, the device would not be portable. In either case, the cylinder represents a mechanical, moving part of the system which is subject to the vagaries of all systems having moving parts. Another limitation of the device described in the BATCHKO patent is that the user (viewer) is unable to interact with the image since the image is enclosed (in a cylinder) and generated on a rotating screen. As will be evident, the present invention overcomes these limitations inherent in a system such as BATCHKO's.
A well known technique for generating three-dimensional images, without involving scanning mechanisms, is known as "holography". In holography, an actual physical object is illuminated with a beam of laser (coherent) light. A reflected beam reflecting off of the object and a reference beam which has not reflected off of the object are combined to interfere with one another. An image of the interference pattern caused by combining the reflected beam with the reference beam is recorded on film. To project the image, a laser beam is split into two components, one of which passes through or reflects off of the film, the other of which does not. In this manner, an image of the object is re-created. From this `generic` description of holography, it is evident that a hologram requires the pre-existence of a physical object in order to record and project its image.
The present invention, as well as the inventions referenced in the aforementioned commonly-owned patents relate to techniques for projecting (displaying) a three-dimensional image of a virtual (non-physical) object, or a sequence of such images, such as has been created by a computer. Evidently, according to the present invention, it is not required (as is the case with holography) to first take a picture of a physical three-dimensional object in order to project an image of a three-dimensional object. As used herein, the image created by the present invention is projected in a "volumetric" format which is distinguishable from an image projected in a holographic format. As used herein, the term "volumetric" and three-dimensional are essentially synonymous.
An area of particular interest is the area of three-dimensional, volumetric displays, particularly computer-generated displays. The have been many problems associated with laser illuminated volumetric imaging. These problems include high "flicker" due to slow scanning speed and modulation. The advent of acousto-optic modulators (AOMs) and deformable mirror display devices (DMDDs) has dramatically improved modulation speeds, but most techniques remain clumsy and slow.